Use correct URL in post_formats_compat()

Description

When getting the URL for the link post format in post_formats_compat(), the incorrect URL value is used. Within the switch statement, when link is the case, the first conditional statement gets the URL that represents the link and assigns it to $url. Within the next conditional, the HTML for the link is composed. Instead of using $url it uses $meta['link_url']. This value may not be set, which will result in a blank URL being printed (e.g., <a href="http://google.com"></a>).